Dedicated high-resolution small animal imaging systems have recently emerged as important new tools for cancer research. These systems permit noninvasive screening of animals for mutations or pathologies and to monitor disease progression and response to therapy. One imaging modality, x-ray microcomputed tomography (microCT), shows promise as a cost-effective means for detecting and characterizing soft tissue structures, skeletal abnormalities, and tumors in live animals. The existing CT systems provide high-resolution images with excellent sensitivity to skeletal tissue and soft tissue, particularly when contrast-enhancing media are employed. However, use of this powerful modality for many important functional studies such as first pass bolus-tracking methodology for volumetric tumor perfusion as well as true whole organ physiologic imaging is limited due to their slower speed of operation (5 to 30 minutes) and limited active imaging area. To address these limitations, we propose to develop a high speed, high sensitivity, large area detector for microCT. The detector will be based on a high efficiency structured scintillator coupled to a modified architecture CCD with specially designed readout to accommodate high frame rates. This will enable imaging of tissue vascular physiology and perfusion in organs as well as conducting functional physiologic studies in small animals.